Wave movements in oceans and large lakes is an important source of energy that can be utilized by harvesting energy from the waves by means of wave power assemblies, also called wave energy converters, which are positioned or anchored at locations with suitable wave conditions.
A number of different types of wave energy converters for harvesting and converting wave energy into electrical energy are previously known. So-called linear generators which, by means of a rope or other connecting means, can convert vertical movements of a buoyant body caused by wave movements into a reciprocating movement of a generator coil or rotor of a linear generator anchored to the ocean or lake floor bed are one example. The reciprocating movement of the generator coil/rotor generates in its turn electrical current in the windings of an adjacent stator of the linear generator anchored to the floor bed.
Another previously known type of wave energy converter comprises a wave energy absorbing buoyant body with an energy absorption and conversion system, which may be placed on the sea floor. The buoyant body is connected to a winch by a winch wire. The winch and the winch wire connect the buoyant body to a reference body below the water surface, such as an anchor platform under the water surface, an anchor on the sea floor, or another anchoring device. As the wave forces causes the buoyant body to move in the longitudinal direction of the winch wire, the winch is forced to rotate, whereupon the rotating motion of the winch axle produced can be converted to electricity by means of an energy conversion system.
Still another type of previously known wave energy converter is instead based on relative movement between, on the one hand, a buoyant body and a thereto attached so-called acceleration tube, and, on the other hand, a working piston reciprocable in the acceleration tube, wherein the relative movement is caused by wave movements in the body of water where the wave energy converter is anchored by means of one or several mooring lines to harvest wave energy. The movement of the working piston can be used for driving for example a pump unit, such as a double-acting hydraulic pump or a hose pump, a hydraulic motor and/or a hydraulic turbine of an energy conversion system, which is disposed within or adjacent to the buoyant body to produce electricity which can be transmitted to an energy storage or electrical grid.
When harvesting electric power from wave energy, it is desirable to be able to place several wave energy converters in an array in the vicinity of each other in a location with particularly favourable wave conditions to achieve an efficient harvesting of wave energy. By arranging for example ten, twenty, or even more wave energy converters in such an array, also called a wave power station, several advantages are achieved. One advantage is that one and the same service vessel can carry out check-ups, repairs and routine maintenance on all wave energy converters in the wave power station without unnecessary transportation, which saves time, personnel and costs. Another advantage is that the electric power generated by the wave energy converters in a wave power station can be transmitted via output cables from the individual wave energy converters to a common connection substation, and via a common cable from the connection substation to shore, which decreases the transmission losses and the risk of cable failures, and reduces the cost for laying power cables.
In wave power stations where the energy conversion system for the individual wave energy converters is placed on an ocean or lake floor surface, or on a submarine structure anchored to the floor surface, which is often the case with e.g. linear generators, it is most natural to also arrange both the connection substation and the common cable leading therefrom on or at the floor surface, i.e. under the water surface. Such a positioning of electrical connection substations and common cables under the water surface, however, may lead to very high costs for underwater equipment and divers, for example when output cables from individual wave energy converters or common cables are to be connected, disconnected or replaced.
In wave power stations where instead the individual wave energy converters are of a type where the energy conversion system is placed adjacent to a buoy or buoyant body floating on or near the water surface, as is usually the case e.g. with wave energy converters with acceleration tubes, it would be possible to eliminate, or considerably reduce, the costs for divers and underwater work associated with connection, disconnection and replacement of cables, if also the connection substation/-stations is/are designed to float on or near the water surface, which is of course advantageous.
However, it had been found that such a positioning of the energy conversion system and/or the common connection substation for the wave energy converters floating at the water surface, which is advantageous per se, implies that the end portions of the cables connected to the individual wave energy converters and/or to the common connection substation will be subjected to large bending stresses caused by wave movements near the water surface, which, in the worst case, can lead to premature fatigue failure of the cables, operational breakdowns and increased costs for repairs and replacement of cables.
The bending stresses on the end portions of the cables caused by wave movements at the surface can to some extent be reduced by placing the lead-out point from or lead-in point to the wave energy converters or connection substations for the cables as far below the water surface as is practically possible, but as a rule this does not reduce the risk of fatigue failure sufficiently to achieve the operational reliability and operational economy desired for this type of marine installations.
Accordingly, in order to reach the best possible operational reliability and operational economy for different floating marine installations or vessels of this surface-based type, especially wave energy converters and their connection substations, it would be a great advantage to be able to further reduce the risk of fatigue failures of the end portions of the cables near the water surface, in a way that does not lead to undesired additional costs for divers and underwater work.
It is previously known to use external bend limiting devices for different power and signal cables, for example electrical connection cords for electrical appliances and optical fibre cables. However, a disadvantage of many of the previously known bend limiters is that they are not designed and dimensioned to be usable in the type of marine installations in question. Another disadvantage of the previously known bend limiting devices is that they usually are configured to be secured to an attachment surface of the installation by means of threads, screws or other joining means which require that a mechanic gets physical access to the joining means to be able to secure or detach such a bend limiter from its attachment surface, which leads to additional costs for divers and underwater work in applications where the attachment surface is located under water.